The study is seen as significant because the Santa Monica group previously has taken pro-immigration views in its studies, which are used widely by national policymakers. Pro-immigration organizations immediately denounced it as a flawed attack on current U.S. laws that promote family reunification, while anti-immigration groups hailed it as another in a succession of reports that have pointed out negative effects.

California is home to 8 million immigrants, who account for 25 percent of the state population, the largest proportion of foreign-born people in the United States. The state attracts about 150,000 to 200,000 of the 1 million people who legally immigrate to the nation every year.

The study found that immigrants to California, particularly those from Mexico and Central America, increasingly are low-skilled and poorly educated. The problem is that the number of jobs suitable to their skills is static.

"There appears to be a growing divergence between current trends in the state's economy and immigration policies that are producing a steady inflow of poorly educated immigrants," wrote two Rand specialists, Kevin F. McCarthy, a demographer, and Georges Vernez, an urban planner.

Vernez said there are about 2.5 million low-skilled jobs in California now, almost exactly the same number as in 1970.

"I don't believe there is much doubt anymore that the opportunities for low-skilled workers in California are disappearing and that almost all of the net new jobs are highly skilled," Vernez said.

"Immigration is not consequence-free," Vernez said. "Immigrants tend to have larger families, and this impacts on education."

He said that although many children of immigrants do well in school, Latino children particularly are lagging behind.

A college education will be crucial to the success of these children, he said, "but the pattern has been that the college-going rate of even Hispanics born here is lower than other groups. . . . If that doesn't change, these young people are going to have a very difficult time."

The study calls for annual national immigration levels somewhere between 300,000 and 800,000, with more screening of immigrants for education levels and employability and less emphasis on family reunification.

She said the call for a reduction in family based immigration "is basically saying that we want you if you have skills, but we don't want your wife and kids."

Munoz said a federal study released in May by the National Research Council concluded that immigrants are a net boost to the U.S. economy while providing a crucial workforce and lowering consumer prices.

"That study showed that negative impacts are overblown," she said.

Munoz, however, agreed that the federal study also showed that immigration can have negative effects in places where there are extremely high concentrations of newcomers, including California.

"These concerns are education issues, not immigration issues," Saenz said. "It's clear that the economy is changing, but that requires a response from the educational system."

But Dan Stein, executive director of the Federation for American Immigration Reform, an anti-immigration group, said the Rand report is "a victory for true scholarship. The fact is that people are hurt by immigration, particularly immigrants who find themselves competing in a job market that holds less and less opportunities for them."